**2.5 Data analyses**

118 Biogas

of operation (20 days), the ADR was inoculated with cow manure (10% v/v) to enrich the methanogenic population. The reactor was stirred by recirculating the FVW twice a day. The pH was initially set at 7 by the addition of a 0.8 N NaOH solution. Later in the process, the pH was naturally regulated by the metabolic intermediates produced during digestion. The bioreactor was kept at room temperature and operated in a fed-batch mode. To avoid inhibition due to metabolic products and to ensure a sufficient supply of organic matter, 2.5Kg of different compositions of fresh feedstock mixtures were fed periodically (approximately every 12-15 days), and an equal volume of exhausted sludge was removed.

A lava rock biofilter was used to evaluate the degradation of H2S from the AD gas stream. The experimental setup for the biofilter used in this study was previously described (Ramirez-Saenz et al 2009). The gas stream was humidified and fed in the top of the biofilter using a mass flow controller. Sample ports were located in the output and input of the gas stream. For H2S degradation experiments, the biofiltration system was fed at the top with an air-diluted gas stream originated from the ADR, as previously reported (Ramirez-Saenz et al., 2009). Periodic water additions (once a week) were used to control moisture loss and to avoid SO4-2 accumulation. Recirculation was provided at a flux of 0.5 L/min over 1 h. All

Different dilutions of the biogas stream produced in the AD at an initial concentration of 3000 ppmv of H2S were prepared by mixing the biogas with humidified air. Two empty-bed residence times (EBRT), 31 and 85 s, were chosen for the performance of the reactor during the H2S and VFA biodegradation tests. Increasing mass loading rates from 99 g/m3h to 400 g/m3h (corresponding to 850 and 3000 ppmv H2S) were used for evaluating H2S removal at both EBRT. Gas samples of the inlet and outlet ports of the biofilter were periodically collected and diluted in 10 L Tedlar bags before taking measurements to determine the H2S and VFA consumption in the biofiltration system. Details of the analysis conditions were

The fruit and vegetable waste samples were analyzed for total solids (TS) and volatile solids (VS) according to the standard methods of the American Public Health Association (APHA,

Biogas production in the anaerobic digester was periodically measured using a water displacement setup in which the biogas was passed through a 5% NaOH solution (Anaerobic Lab Work, 1992). Biogas samples were taken periodically from the gas collection lines prior to the water displacement setup, and the gas composition was analyzed using a gas chromatograph (GowMac Series 550, Bethlehem, PA) equipped with a thermal conductivity detector. A CTR1-packed column (Alltech Co., Deerfield, IL) was used for the analysis. The analysis conditions were the same as those reported previously (Garcia-Peña et al., 2009). VFA samples were analyzed in a gas chromatograph (Buck Scientific, East

experiments were conducted at room temperature (20-25ºC).

**2.2.3 H2S elimination tests in the biofilter** 

previously reported in Ramirez-Saenz et al., 2009.

Norwalk, CT) as previously reported (Garcia-Peña et al., 2009).

**2.3 Analytical methods** 

2005).

**2.2.2 Biofiltration system** 

The data obtained for the microbial population by DGGE were further analyzed by Jaccard's (3) and Sorensen-Dice´s (4) indexes. Similarity indices are frequently used to study the coexistence of species or the similarity of sampling sites. A matrix of similarity coefficients, between either species or locations, may be used to analyze changes in microbial populations over time or at different locations (Real and Vargas, 1996). Jaccard's index is one of the most useful and widely used indices to determine similarity between binary samples. Jaccard's index may be expressed as follows:

$$f = \frac{n\_{AB}}{n\_A + n\_B - n\_{AB}} \tag{3}$$

where ��� is the number of bands in both samples A and B, �� is the number of bands present in sample A, and �� is the number of bands present in sample B.

Sorensen-Dice´s index, also known as Sørensen's similarity coefficient, is also used to compare the similarity of two samples. It can also be applied to the presence/absence of data. The index is described by the expression, the terms of the equations are the same as describe above:

$$\mathcal{S}\_{\mathcal{D}} = \frac{2n\_{\mathcal{AB}}}{n\_{\mathcal{A}} + n\_{\mathcal{B}}} \tag{4}$$
